Effect of Ni on the ion-selectivity of rust layer on low alloy steel

In order to clarify some features of atmospheric corrosion mechanisms, mild steel and two kinds of low alloy steels (1%Ni and 4%Ni-bearing steel) were investigated using 0.3%NaCl solution in wet/dry cyclic corrosion tests to simulate the coastal environment. The cross-section of rusted steels was analyzed by ESEM after 100 wet/dry cycles. The ion-selective permeability of rust layers on steels was investigated by measuring the distribution of Cl and Na element in the rust layer using EDXA. The results showed that the addition of Ni improved the ion-selective property: the rust layer of mild steel was anion-selective; the rust layer of Ni-bearing steel mainly was anion-selective, and its anion-selective property decreased with increasing content of Ni. The cation-selective property of the rust layer of Ni-bearing steel emerged when the content of Ni exceeded 4%.